I’m probably not the person to ask, to be honest. Lemmy as I understand it is the protocol that exchanges the information about posts, etc. The post content is stored and shared as plaintext, but Lemmy also has instructions about how a UI should interpret the text and serve it to the user.
Ideally, the same text should appear consistent across any UI. Obviously, some apps will use different fonts and colors and may interpret the style of an element differently.
maegul